The ratio of roll gears depend on both the pressure angle of the part and, the pressure angle of the cutter.This is designated as K1.K1 = (cos pr.angleof the part/cos pr angle of cutter) Nc/2 = ((DP)(Ao)/(K1)). If Nc/2 is less than 15,the selection constant is 25.Above 15 the constant is 50.The decimal ratio is as follows,(2.0(Nc/2)/selection constant)) = decimal ratio.If Nc/2 is 15 or less, change selection gearin the cradle roll .Look at chart on cradle roll gear door for details.If you don't have the selection gear, Nc25 ratiodivided by 2 = Nc50 ratio.I hope this helps Dogballz99